1. Field of the Invention
The invention relates to exercise and sports, and in particular, to applications in which lactate concentration is assessed in a human body in connection with exercise.
2. Brief Description of the Related Art
Efficiency of an exercise can be described as exercise intensity in relation to time, which intensity can be observed e.g. as heart rate frequency in relation to time. When momentary intensity of exercise is observed in this manner, a momentary assessment of stress is obtained. The effect of long-term exercise stress depends on the individual such that a person having good condition endures exercise stress better than a person having poor condition. For instance, it is possible that each one is able to perform the same exercise at the same intensity, but the individual effect of the exercise is different: the person having good condition is not liable to considerable fatigue, whereas the person having poor condition performs the same exercise at the extreme limits of capacity. The effect of the momentary stress on the individual and on the individual stress level experienced during exercise depends on preceding stress.
In training, it is important to know the amount of cumulative stress, which increases under hard stress and decreases at rest. Concentration of lactate, i.e. lactic acid, in blood represents well the cumulative stress. The amount of lactate is the only indicator by which the cumulative stress can be measured in practice. Recovery after exercising is important both to metabolism and to muscle care. Stress pain resulting from exercising can be reduced significantly by well-performed recovery exercise, whereby recovery is achieved in shorter time and the capability of the muscles and the system to perform the next exercise improves substantially. The most important function of the recovery exercise is to remove the accumulated lactic acid, i.e. lactate, if any, from the body quickly and efficiently, so that the lactate could not cause pain or post-stress conditions in the muscles. This calls for a method by which the amount of lactate can be assessed in the body on a continuous basis.
According to the prior art, the amount of lactate can be measured by taking a blood sample that is analyzed. The prior art has disadvantages. The measurement of lactate from blood is painful, discrete, slow and often requires a complicated measuring arrangement.
The object of the invention is to provide an improved method for assessing lactate concentration in the body. This is achieved by the method to be described in the following. The method concerns assessing the lactate concentration in the human body in connection with exercise. The method measures a person""s heart rate information in the form of one or more heart rate parameters to be included in a mathematical model as input parameters and, by means of a mathematical model which models the lactate concentration in the body, forms a lactate concentration level of the person""s body as an output parameter of the model to be presented in the assessment of the lactate concentration of the body.
The invention also relates to a heart rate measuring arrangement. The heart rate measuring arrangement comprises measuring means for measuring heart rate information, forming means for forming an assessment on the basis of the measured heart rate information of the lactate concentration of the body, presenting means for presenting the formed assessment of the amount of lactate in the body.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention thus relates to a method and equipment for assessing lactate, i.e. lactic acid, in the body. The method of the invention is advantageously implemented by means of a mathematical model. In the description of the invention, the mathematical model refers to a plurality of mathematical operations and rules, by which output parameter values are obtained from input parameter values. Mathematical operations include e.g. arithmetical operations, such as addition, subtraction and multiplication. It is also possible to implement the mathematical model as a table or a database, whereby an output parameter value corresponding to a given input parameter value is read directly from the database. The model may include a plurality of submodels, but it is obvious that the invention is not restricted to how many submodels the model comprises. In one embodiment of the invention, the mathematical model is a neural network, but the invention is not restricted thereto, however.
The input parameters of the model include one or more heart rate parameters representing the person""s heart rate, such as the heart rate calculated from heart beat frequency, standard deviation of the heart rate, change rate of the heart rate or a similar parameter that can be calculated from the heart rate. According to one embodiment, the input parameters of the model also include one or more physiological parameters which refer to the person""s age, weight, height, gender or other physiological property. In one preferred embodiment, the model""s input data comprises one or more stress parameters, such as the runner""s speed, resistance of an exercise bike or activity measured with an acceleration transducer or the like. By means of the heart rate and physiological parameters it is possible to provide an assessment of the person""s physical condition, for instance, on the basis of the maximal oxygen uptake. According to one preferred embodiment of the model, a user""s stress level during exercise is formed on the basis of the heart rate information and optionally the stress and user information, on the basis of which stress level the lactate amount in the body is assessed. Then there is no direct correlation between the heart rate information and the lactate, but the connection is formed through a stress level definition, which stress level can be represented by a quantity of performed intensity during the last hour.
In connection with the present description of the invention, an exercise, i.e. sporting performance, refers to a physical performance, at least part of which is carried out at a workload level exceeding the anaerobic level, whereby lactate is accumulated in the muscles of the person""s body. Lactate concentration can also be assessed for a given period of time, for instance, for a few hours before and after the exercise, so the application of the invention is not only restricted to the moment of exercise. It can be assumed that the exercise divides into the following phases: warm-up, active phase, recovery phase when the exercise is preceded and followed by a rest. Different phases can be defined and distinguished, for instance, on the basis of heart rate levels and/or workload levels. Then, for instance, the recovery phase can be defined as a performance level when the heart rate is dropped from 130 beats per minute to a resting level of 70 beats per minute.
In the solution of the invention for assessing the lactate concentration in the body, the person whose lactate concentration is to be monitored advantageously wears a heart rate monitor. The heart rate monitor is a device employed in sports and medicine, which measures human heart rate information either from an electrical impulse transmitted by the heart or from the pressure produced by the heart beat on an artery. Generally, the heart rate monitors have a structure comprising an electrode belt to be fitted around the user""s chest measuring the heart rate by means of two or more electrodes. The electrode belt transmits the measured heart rate information inductively as one or more magnetic pulses per heart beat, for instance, to a wrist-worn receiver unit. On the basis of the received magnetic pulses, the receiver unit calculates the heart rate and, when needed, other heart rate variables, such as moving standard deviation of the heart rate. Often, the receiver unit, i.e. the wrist monitor, also comprises a display for displaying the heart rate information to the exercise performer and a user interface for the use of other facilities of the heart rate monitor. In the above-described situation, the heart rate monitor refers to the whole formed by the electrode belt and the receiver unit. The heart rate monitor can also be a one-piece device, i.e. such that also the presenting means are located on the chest, whereby there is no need to transmit the information to a separate receiver unit. Further, the structure of the heart rate monitor can be such that it only comprises a wrist-worn monitor which operates without the electrode belt to be fitted around the chest measuring the heart rate information from the vessel pressure. In the description of the invention, the heart rate measuring arrangement refers to the above-described heart rate monitor solutions. The heart rate measuring arrangement also comprises the solutions, in which heart rate information is transmitted to an external computer or to a data network, which has presenting means, such as a computer screen, for presenting the information measured or generated by the heart rate monitor.
According to the invention, one or more mathematical models and other functions required by the model are advantageously implemented by means of software for a general-purpose processor of the heart rate monitor. The models and functions can also be implemented as ASIC, with separate logic components or in another, corresponding manner. In a preferred embodiment of the invention, the heart rate monitor comprises entering means for entering input parameters. The input parameters to be entered include, for instance, the user""s physiological parameters and stress parameters representing the workload of the exercise. The entering means can be, for instance, a keypad of the heart rate monitor, display equipment that supports control, speech control, a telecommunication port for external control or the like. The heart rate monitor also advantageously comprises a display for displaying the lactate concentration to the user, exercise instructor, trainer, doctor or the like. Instead of the display, the lactate concentration can be communicated also e.g. by speech control, via a telecommunication port for transmitting the information to an external device, such as computer, or in another corresponding manner. In one embodiment, the lactate concentration during exercise can be stored in a memory of the heart rate monitor, wherefrom the information can be outputted afterwards.
An advantage of the invention is non-invasiveness, i.e. when assessing the lactate concentration there is no need to take blood samples, which is painful and slow and hampers the performance of exercise. By means of the invention, the amount of lactate in the body can be monitored on a continuous basis as compared with prior art methods, whereby discrete evaluations of the lactate concentration are obtained. By means of the invention, it is further possible to adjust the workload of the exercises to a level which is optimal for the lactate to accumulate in the body and to be removed from the body.